Many computer systems use dynamic random access memory (DRAM) as system memory to temporarily store an operating system, critical applications, and data. With widespread use of multi-core processors, particularly, in servers and workstations, higher capacity and faster memory devices are needed to catch up with the computing power of these processors, thereby reducing the processor-memory performance gap and allowing the applications to use the full processing speed of modern processors.
One way to narrow the processor-memory performance gap is to develop innovative technologies to enhance characteristics of DRAM chips in terms of capacity and bandwidth. Yet another way is to increase storage capacity by stacking memory chips, while using existing DRAM technologies. For example, in servers and storage applications, depth stacking can be used to obtain high memory densities in a smaller space and most likely at a lower cost. Other industrial or embedded applications may demand different memory requirements, but typically high-density depth stacking is needed where space is constrained, therefore requiring more memory capacity on the same or a smaller memory module form factor.
Stacked memory dies can be formed by mounting two or more memory dies, one on top of the other, and interconnecting them using through-silicon-vias (TSVs). Conventional solutions use substantially identical memory dies derived from the same mask set to form memory stacks. While these solutions allegedly work for their intended applications, there are a number of disadvantages associated with these solutions. For example, by using substantially identical dies in the stack, certain cost saving opportunities may be lost. For instance, there are some features that may only be needed on one of the memory dies of the stack. Such features may not have to be fabricated in the other memory dies of the stack. On the other hand, if some of these features are omitted on all of the dies, the substantially identical memory dies used in conventional memory stacks may not be viable for use as stand-alone memory devices in a cost effective manner.
Thus, the need exists for a high density memory device formed by stacking memory dies which are not substantially identical, therefore alleviating the disadvantages of the conventional solutions. Embodiments described herein satisfy this need.